1. Field of the Invention
The present invention relates in general to electronic ballasts of the high power factor-constant power type, and more particularly to an electronic ballast for starting, lighting and maintaining a variety of discharge lamps such as a neon lamp, a mercury lamp, a natrium lamp, a metal lamp and etc.
2. Description of the Prior Art
A ballast for a discharge lamp being widely used now, more particularly a ballast for a high voltage discharge lamp employs a magnetic circuit, namely, a transformer. In such a ballast of the magnetic circuit type, the transformer is provided with copper wires which have a predetermined thickness to cope with a high voltage being applied to a load and a large amount of current flowing therethrough, and a core which is large in size to have a reactance at a low frequency of 50/60 Hz. With this construction of the transformer, the ballast of the magnetic circuit type is disadvantageously very heavy in weight and large in size. This disadvantage becomes more prominent as the discharge lamp as the target to be driven requires a higher power. Also, the ballast of the magnetic circuit type has another disadvantage in that a supply power thereto is partially consumed due to an eddy current and a hysteresis loss of the core, resulting in generation of a large amount of heat in the ballast and, thus, waste of energy.
The ballast of the magnetic circuit type has widely been used until now in spite of the disadvantages that it has a large amount of power loss and is large in size and heavy in weight. However, a demand for power saving appliances has recently been increased according to a rapidly increased demand for power. More particularly, it has keenly been required to save energy in industrial and public high power electric appliances. With commercialization of an electronic circuit type-ballast for a fluorescent lamp based on such a trend, in the discharge lamp field, it has been intended to change the magnetic ballast circuit into the electronic ballast circuit for the purpose of removing the power consumption resulting from the features of the discharge lamps.
One example of conventional ballasts of the electronic circuit type is an electronic ballast for a high voltage discharge lamp, which is shown in Korean Patent No. 44,447, filed on Jan. 7, 1989 and issued on Sep. 19, 1991. However, in this electronic ballast, since an alternating current (AC) input voltage is full-wave rectified, smoothed and then applied directly to the circuit, a power factor at a power input stage is bad and an amount of power supplied to a load is varied according to a variation in the input voltage. For this reason, the electronic ballast requires an input current larger than that in the existing magnetic ballast. Also, the variation in the supply power to the load or the discharge lamp results in a reduction in the life of the discharge lamp.
Furthermore, the conventional electronic ballast has no protection means against a short circuit of a load stage or an abnormal high temperature condition, resulting in an electric damage in the circuits.